The present invention relates to the field of optical devices, and more particularly concerns a dual optical path rotary joint suitable for optogenetics applications and the like.
1. Field of the Invention
Fiber-optic rotary joints (FORJs) are well-known optical devices. FORJs allow uninterrupted transmission of an optical signal across a rotating interface created between two optical fibers as one is rotating about its axis and the other is stationary. Various types of FORJs exist including single path and multipath (e.g., dual path) FORJs. Single path ORJs have a single input and a single output port, and may be realized using two coaxially and oppositely aligned optical fibers terminated with lenses, such that the two fiber-to-lens assemblies are rotatable relative to each other, for example by using an appropriate bearing configuration.
In contrast, multipath FORJs have multiple input and/or output ports and multiple paths extending therebetween. Some multipath FORJs have optical paths that can overlap or merge with one another along a part thereof, for example in the case where two beams of different wavelengths are combined, passed from the static to the rotating part of FORJ, and finally divided into two beams of equal intensity and spectral content. In such FORJs, half of the light is lost if the two initial beams have the same wavelength or if the direction of light propagation is reversed. Truly independent dual path FORJs, that is, FORJs that can connect two rotating optical fiber ports with two non-rotating optical fiber ports regardless of their wavelength band, typically require more complex arrangements than their single path or partially shared dual path counterparts.
2. Background of the Invention
FORJs have been used in various industrial, medical and military applications including robotics, material handling systems, fiber optic cable reels, medical systems, and security systems. In particular, in recent years, FORJs have become useful devices for optogenetics applications by providing simple and inexpensive passive tools for connecting light sources to freely moving laboratory animals via optical fibers. Optogenetics is a technological field where genetic and optical methods and devices are combined to monitor and control targeted biological functions and events in specific cells (e.g. neurons, heart muscles cells) of living tissue. Optogenetics is particularly well adapted for in vivo studies of biological functions in mammals and other animals. Early optogenetics applications typically involved sending light from a laser or a light-emitting diode (LED) source along an optical fiber toward the brain of a laboratory animal, typically a mouse or a rat. In recent years, however, these simple optical links have evolved into more complex systems, which now include fiber-coupled light sources and their drivers, FORJs for in vivo experiments, light shutters or modulators, beam splitters, fiber-optic patch cords, various fiber-optic cannulas with implantable fibers, and the like.
In this regard, FORJs facilitate optogenetics experiments involving a freely moving animal by allowing the unimpaired movement of the animal, while maintaining satisfactory transfer of optical power between the two fibers and reducing the chances of damaging the fiber due to excessive torque. However, in the context of optogenetics applications where it is desirable to deliver light coming from two light sources to two distinct output points on a live animal, existing dual path FORJs suffer from several drawbacks such as partial shading of one of the light channels as in U.S. Patent Application Publication No. 20070217736 or use of glass tube walls as optical window for the passage of the collimated light beam as in U.S. Pat. No. 4,725,116 that causes aberrations and related optical losses and is not well-suited for deposition of internal and external AR coating. Both approaches are based on gradient-index lenses known as SELFOC lenses that have very limited choice of focal lengths, spectral windows and numerical apertures and are not suited for larger fiber diameters. (SELFOC is a trademark of Nippon Sheet Glass Company Limited Corporation.) In addition, those gradient index lenses require the fiber to be glued to the lens surface, which exclude the possibility of providing connectors at the rotary joint. In experiments with live animals it is common that fiber optic patch cord are being chewed, bitten or otherwise damaged by the animal and that requires change of the patchcord. If the fiber is permanently attached to the FORJ or pigtailed then the FORJ may need to be replaced, while in a version having connectors only the patch cord needs to be replaced. And finally, it is desirable that optogenetics applications include either low friction passive rotary joints driven by the animal movement or motorized rotary joints preferably including appropriate animal movement sensors.
There therefore exists a need in the art for a passive, cost-effective and compact dual optical path rotary joint capable of reliably and independently delivering two light signals from two light sources to freely moving targets or receiving independently light signal from tissue.